Both companies have intimate knowledge of the manufacturing processes relevant to their designs but they have avoided the cost of setting up their own wafer fabs and worked with TSMC.
It is a financial formula that works. The fabless get a faster, lower-cost route to market that helps them compete against the IDMs while the foundries acquire process know how, which they may one-day be able to offer to other MEMS startups. Although the true standardization of manufacturing processes has yet to happen in the MEMS sector, it appears the economic benefits of disaggregation into a fabless and foundry duality will not be denied.
Of course, these things are never simply black and white. In logic production IDMs have co-existed with foundries for many decades. In last few years the interdependence of design and process has increased, as have the variety of processes (planar CMOS, FinFET CMOS, FDSOI and other variants). Similarly in the MEMS domain ST's replacement at the top of the MEMS vendor ranking is Robert Bosch, which is a classical IDM with its own dedicated MEMS wafer fab.
Nonetheless, expect future MEMS startups to be predominantly fabless. They will be looking for foundries to work with them on process development and carry the cost of expensive wafer processing machines and the likes of TSMC and Globalfoundries appear ready to step forward to do that. IDMs such as Bosch and STMicroelectronics will also be tempted to keep wafer fabs full by running third-party MEMS wafers which brings them into the part-time foundry category.
This financial slope led to the foundry business solution in digital logic and it will do the same for MEMS and it probably won't take decades to do it.
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